Tunnel kiln and process of heating ceramic articles



April 7, l931- IHARTER E-r Al. 1,799,296

TUNNEL KILN AND PROCESS OF HEATING CERAMIC ARTICLES 2 vSheecs-Sheec l Filed Dec. 51j 1926 kw x@ \N o, mw ww o g o April 7, 1931. HARTER ETAL 1,799,296

TUNNEL KILN AND PROCESS OF HEATING CERAMIC ARTICLES Patented Apr. 7, 1931 l UNITED STATES PATENT OFFICE ISAAOHABTEB, OF DONGAN HILLS. NEW YORK, ANTHONY I. XOHLER, OF EAST LIVER- P0012,` OHIO, AND FREDERICK NORTON, OF CAMBRIDGE, 'IASBACHUSm BIGNORS TOTHE BABCOCK @c WILCOX COMPANY, OF BAYONNE, NEW A OOR- rona'rron or NEW :mam

, TUNNEL xine 'Aun rnocnss or HEATING CERAMIC Amicus application nea December s1, `issus.` serial no. risalta.v

r1 his invention relates toa tunnel kiln in which ceramic articles are burned, and will be understood from the descriptiony in connection with the accom anying drawings,

5 in which Figs. l and 1a s ow a longitudinal l sectional elevation throu h the kiln, Fig. la being a continuation of Fig. 1; and'Fig. 2 is a sectionalon the line 2--2 of Fig. 1 on an enlarged scale.

The tunnel kiln which illustrates an einbodiment of our invention is composed of threesect-ions or zones, thev section being the preheating zone, the section 1 1` being the burning or ring'zone and section 12 being the cooling zone. Parts are broken awayin Figs. 1 and 1a to avoid duplication, and to vshow the device more clearly, thus making these iigures much shorter than they would otherwise be. Parallel track rails 13 extend longitudinally through the tunnel with their ends resting upon cross supports orpillars 14. The upper surfaces of the rails 13 are `smooth and are provided with grooves 15 for lubricant, whic may be forced -thereinto through the holes 16. The space between the rails 13 may be left open and the rails connected by means of transverse braces 17.

The articles to be fired are passed through the kiln on cars, each one of which comprises i a metal plate or base 18, preferably somewhat wider than the distance between the outer edges of the rails 13. 'Thetop side of the plates 18 may be provided' with suitable means such as metal strips 19, for example, for retaining a layer of refractory or insulating 18, the bottom layer being provided with grooves to it over the strips 19, and each successive layer being preferably of amore highly refractory material than the layer below. n the top layer of refractory material 20 may be placed longitudinal parallel saddles i 21 of suitable refractory material. ri'hese saddles are s aced apart and may taper upwardl ,the at lupper surfaces thereof being rovi ed for receiving the articles to be urned. 'Bricks 22 may be laid edgewise on the saddles to provide channels between the bricks for a purpose to be described. The

riages and force themforward.

heat in the tunnel does not readily radiate to bottom of the late -18 is providedv with uides 23, which fit etween the rails 13, an each plate 18 is also provided with a =1ug 24 near the middle thereof. A pair of Scrapers 25 are located beneath and attached to the plates 18 outside of the rails 13 at an Yangle to the rails, so that they will scrape off and remove foreign material from the surfacesoutside of the rails. The cars are pushed through the tunnel one behind the other, in any convenient and well known manner, so that each one pushes the row in front of it, such as by a motor driven chain 25, for example, passing over sprockets 26 and rovided with lugs 27 that catch behind the ugs 24 on the car- The top 30 and side walls 31 of the tunnel are made of refractory material, covered on the outside with insulatin materials 3:2. Refractorymaterial 33exten sacrossthe spaces from the side walls tothe rails 13. The upper surface of the material 33 is made iiat, and holes with cover plates' vmay be provided so that forei n material can be scraped into these holes y means of the scra rs 25, from which holes r the foreign materlal can be withdrawn by 'removing the cover plates. The distance between theyeside walls 31 is only slightly greaterthan-the width of the cars, so that the metal plate 18 orl the rails 13. v

The preheating section 10 of the tunnel may be of uniform cross section throughout its length, and merges into the. firing section 11. The firing section 11 comprises a combustion chamher35 which is an enlargement of the tunnel proper and gradually increases in cross section in the direction in whichthe cars travel. One or more fuel burners 36 may be provided for the combustion chamber 35 that has a peep hole 37.

The-cooling' section l12 is provided with an open exit end 40 for, the cars. This sectionV may be shaped similar to section 1 0, and one or more openingsv 41 are provided at suitable points in this section, from .which openings a conduitor conduits 42 extend to an eihauster 43. An outlet 44 from this exhauster ectends into the space 45 that communicates 100 through the opening or passage 46 with the combustion chamber 35.

A chamber 47 is provided at the front end of the preheating section 10 and communicates therewith. This chamber is provided with a stack 48 through which the waste products of combustion are discharged. An exhauster 49 is placed in the stack 48 and means may be provided to baille or close the opening of this chamber, such as a plate 50, provided Awith slots or openings through which the rows 22 of bricks may ass, extends.

across the front end of the cham er 47 The operation is as follows: The ware to be burned, such as brick, for example, is laid upon the saddles 21 in longitudinal rows, so as to provide open spaces or channels between the same. The cars are pushed through the tunnel and as each car enters the tunnel, the car -itself, together with the saddles 21 and the bricks stacked thereon, as shown in Fig. 2, almost fill the tunnel, so that only narrow spaces are left between the load and the top and side walls of' the tunnel, with longitudinal channels between the rows of brick 22I on the saddles 21. When the car enters the firing section 11, the hot products of combustion from the fuel, that emerges from the burners 36, are directed downwardly at an angle to the horizontal and opposite to the direction of travel of the car. In this way the hot gases from the combustion chamber of the tunnel plass along the sides of the brick and preheat t e same substantiall uniformly, while the tracks 13 and metal ottoms 13 of the cars are effectively shielded from excessive heat. Our investigations have shown that the hot gases should be directed somewhat downwardly and that the velocity of the hot gases should be sufficiently high to avid a greater temperature difference than about 25 F. throughout the cross section of the' tunnel taken at any one point vertically and at right angles to its length. An average velocity of the gases in excess of fifteen feet r second has been found to be sufficient. he vel'ocity at the high temperature end of the preheating section may be in excess of twenty feet per second. It has been found that the brick may be heated substantially uniform ly in this manner in excess of 3000 F. in this chamber, while permitting the same to travel therethrough at about Vten feet per hour. As"

the cars pass beyond the combustion" chamber they enter the section 12 where cooling begins. A preliminarily cooling of the bricks is obtained by radiation in the first portion of this cooling section. Air entering the end 40 of'the'tiinnel and passing between the rows of bricks further cools them. The heated air then passes through the holes 41, through the exhauster 43, the outlet 44 into the air space 45, where it is used for combustion of the fuel from burners 36 in such amount'as may be required for combustion. When the cars emerge from the tunnel they may pass on to the rollers 49 where the loads can be removed, and the cars may be returned to the front of the tunnel in any convenient way. The open space between the-rails 13 enables cool air to come into contact with these rails and the lower surfaces of the` metal plates 18 thus tending to keep them cool throughout their entire passage through the tunnel.

We prefer to prevent the passage of air or gas between the combustion zone and the cooling zone by maintaining a pressure in the combustion zone balanced with respect to the pressure in the cooling zone. That is, the pressure at 41 should preferably be maintained the same as that in the furnace 35 to prevent air or gas from iowing between the two. However, by maintaining a somewhat lower ressure in the combustion chamber 35 than t at in the cooling zone 12, all or a part of the air for combustion may be passed directly from the cooling Zone 12 into the combustion chamber 35, at such'point or points as may be desirable to suit conditions of fuels and combustion. These pressures will be negative or below atmospheric with the arrangement shown in the drawings. Also,

the pressure at the cool end of the preheat' accomplished by means of the exhauster 49 l in the stack 48.

While theair has been described as entering the cooling section at the end thereof and passing along in Contact with the bricks to cool the same, we may pass the air through a Jacket surroundin the cooling section, which airis ermitte ti'eitlier enter the furnace for com ustion purposes or exhaust into the atmosphere after performing ,its work of cooling the jacket. Also, instead of having the pieheating section of uniform cross section from one end to tli'e other, this section may be made of'gradually decreasing cross section toward'the end where the bricks enter, so that as the hot gases become cooled and their volume therefore decreased, the velocity of the gases can be thereby kept approxlimately constant from the furnace section to the end of the kiln. Alsothe cooling section may be made of gradually decreasing cross section toward the exit end 'for a case a baie may be provided near the .opening between the .combustion chamber 35' and the cooling section 12 to prevent the air from passing directly into the combustion cham-- ber from the cooling section.

' uniformi We claim:

1. A process of heating ceramic articles in a tunnel kiln, which comprises providing a uniform temperature throughout any cross section in the preheatingzone of said tunnel kiln by passing heated gases through said preheating zone and passing said articles through said tunnel kiln in a direction opposed t0 the gas flow, said articles being arranged to provide channels on both sides of said articles, said channels and articles occupying substantially the entire cross sectional area of said preheating-zone.

2. A process of heating ceramic articles in a tunnel kiln, which comprises providing a of temperature throughout any cross section in the preheating zone of said tunnel kiln by passing heated gases through said preheating zone at a velocity sufcient to lcounteract the tendency ofthe heated gases to form thermal layers and passing.

said articles through said tunnel kiln in a direction opposed to the gas flow, said articles being arranged to rovide channels on both sides of said artic es, said channels and articles. occupying substantially the en; tire cross sectional area of said preheating zone.

3. A process of heating ceramic articles in a tunnel kiln, which comprises providing a uniformity of temperature throughout any cross section in the preheating zone of saidtunnel kiln by passing heated gases through said preheating zone ata velocity suilcient to counteract thetendency ofthe heated gases to form thermal layers and passing said articles through the tunnel kiln in a direction opposed to ther gas flow, said articles being arranged to provide` channels on both sides of saidv articles, said channels and articles occupying substantially the entire cross-sectional area of said preheating zone, said channels being of substantially equal crosssectional area.

4. A process of heating ceramic articles in a tunnel kiln, which comprises providing a uniform temperature throughout any cross section in the preheating zone of said tunnel kiln by passing heated gases through said preheating zone and passing said articles through said tunnel k iln in a direction opposed to the gas flow, said articles being arranged to provide channels on both sides of said articles, the cross-sectional area within said kiln above said articles being less than the cross-sectional area of one of said channels.

5. A process of heating ceramic articles in a tunnel kiln, which comprises providing a uniformity of temperature throughout any cross section in the` preheating zone of lsaid tunnel kiln by passing heated gasesv through said preheating zone at a velocity suicient to counteract the tendency of the heated gases to form thermal layers and passing said articles through said tunnel kiln 1n a direction opposed to the gas flow, said articles being arranged to provide channels on both sides of said articles, said channels and articles occupying substantially the entire cross-sectional area of said preheating zone, whereby said articles are uniformly heated by direct contact with said gases, and subsequently heating said articles in the combustion zone of said tunnel kiln toa temperature in excess of 2800 F.

6. A process of heating ceramic articles in a tunnel kiln, which 4comprises providing a uniformity of temperature throughout any cross section in the preheating zone of said tunnel kiln within 25- F. by passing heated gases through saidpreheating zone at a velocity suliicient to counteract the tendency of the heated gases to form thermal layers and passing said articles through said tunnel kiln in a direction opposed to the gas flow, said articles being arranged to provide channels on both sides of said articles, said channels and articles occupying substantially the entire Icross-sectional area of said preheating zone, whereby said articles are uniformly Ivheated by direct contact with said gases, and

subsequently heating said articles in the combustion zone of said tunnel kiln to a temperature in excess of 2800 F.

7. A process of heating ceramic articles in a tunnel kiln, which comprises providing a uniformity of temperature throughout an'y cross section in the preheating zone of said tunnel kiln within'25 F. by passing heated gases through said preheating zone at an average velocity greater than fifteen feet per second, and passing said articles through the tunnel kiln in a direction opposed to the gas flow, said articles being uniformly heated by direct contact with said gases, and subsequently heating said articles in the combustion zone of said tunnel kiln to a temperature in excess of 2800 F.

8. A process of heating ceramic articles in a tunnel kiln, which comprises prbviding a uniformity of temperature throughout any cross section in the preheating zone of said tunnel kiln within 25 F. by passing heated gases through said preheating zone at a velocity at the high temperature end of the preheating zone in excess of twenty feet per second and passing said articles through the tunnel-kiln in a direction opposed to the gas flow, said articles being uniformly heated by direct contact with said gases, and subse- `quently heating said articles in the combusin the combustion zone balanced with respect to the pressure in the cooling zone.

10. In the operation of a direct fired tunnel kiln having a combustion zone with a free opening into an induced draft cooling zone, the process which comprises preventing the passage of air or gas between the combustion zone and the cooling zone by maintaining a negative pressure in the combustion zone, equal1 to the lowest negative pressure in the cooling zone.

11. In the operation of a direct fired tunnel kiln having a preheatin zone with a free `opening into a combustion zone which in turn has a free opening into a cooling zone, the process which comprises preventing the passage of air or gas between the combustion zone and the cooling zone by maintaining pressure in the combustion zone balanced with res ect to the pressure in the cooling zone, an maintaining a negative draft pressure at the low temperature end of the preheating zone which is less than the pressure' 1in the combustion zone by an amount equal to the draft loss through the preheating zone.

12. In the operation of a direct fired tunnel kiln having a preheating Vzone with a free openin into a combustion zone which in turn has a ree opening into a cooling zone, the process which comprises preventing the passage of air or gas between the combustion zone and the cooling zone by maintaining pressure in the combustion zone balanced with respect to the pressure in the cooling zone and maintaining a negative draft pressure at the low temperature end of the preheating zone which is less than the pressure .inl the combustion zone by an amount equal to the draft loss through the preheating zone, and preventing the admission of an appreciable amount of air to the preheating zone through the end opposite the combustion zone.

13. In the operation of a direct fired tunnel kiln having a combustion zone and a cooling zone, the process which comprises causing the passa e of air or vgas from the cooling zone into t e combustion zone by maintaining a pressure in the combustion zone lower than that in the cooling zone.

14. In the operation of a direct ired tunnel kiln having a combustion zone with a re stricted opening into a cooling zone, the proccss which comprises causing the passage of air o r gas between the combustion zone and the cooling zone by maintaining a negative pressure in the combustion zone with respect to the pressure in the cooling zone.

15. In the operation of a direct fired tunnel kiln having a preheating zone with'a free opening into a combustion zone which 1n turn has a restricted opening into a coolmlg zone, the process which comprises causing t e p assage of air or gas between the combustlon zone and cooling zone by maintaining a higher pressure in the cooling zone than in the combustion zone, and maintaining a negative draft pressure at the low temperature end of the preheating zone which is less than the pressure in the combustion zone by an amount equal to the draft loss through the preheating zone.

16.' In the operation of a direct fired tunnel kiln having a preheating zone with a free opening into a combustion zone which in turn has a restricted opening into a cooling zone, the process which comprises causing the passage of air or gas between the combustion zone and cooling zone by maintaining a higher pressure in the cooling zone than in the combustion zone, and maintaining a negative draft pressure at the low temperature end of the preheating zone which is less than the pressure in the combustion zone by an amount equal to the draft loss through the preheating zone, and preventing the admission of an appreciable amount of air to the reheating zone through the end opposite t e combustion zone.

17. In a tunnel kiln, in combination, a metal track having a smooth surface and a space between the edges of said track, and a can' adapted to slide on said track and close the space thereacross.

18. In a tunnel kiln, in combination, a track comprising spaced rails having a smooth surface and a car adapted to slide on said tracks and close the space between said rails, said car extending beyond said rails on both sides.

19. In a tunnel kiln, in combination, a metal track having a smooth surface and a space between the edges of said track, and a car having a metal bottom adapted to slide on said track and close the space thereacross.

20. In a tunnel kiln, in combination, a track comprising spaced rails having a smooth surface, and a. car adapted to slide on said track and close the s ace between said rails, the s aces between t e outside of said rails and t e walls of said tunnel also being closed.

21. A car for a tunnel kiln comprising a sliding metal base covered with layers of insulating and refractory materials of different degrees of conductivity.

22. A car for a tunnel kiln comprising a sliding metal base covered with layers of insulating and refractory materials having spaced longitudinal supports for ware along t e top thereof.

23. A car for a tunnel kiln comprising a metal base covered with layers of insulating and refractory materials having spaced 1ongitudinal su ports for ware along the top thereof, sai supports being wider at the bottom than at the to l 24. In a tunnel kim, a track having a smooth surface, cars to slide thereon, means for lubricating said surface, and means to momo@ prevent said track from becoming ovcrhoated. 25. 1n a tunnel kin, o, track having a. smooth surface, cars having metallic bases, and moans to revent said track from becom- 5 ing overheat-@ by cooling the same with air.

ISAAC HARTER. ANTHONY M. KHLER. FREDERICK H. NORTON. 

